Apparatus for striping inside seams of cans

ABSTRACT

A method and apparatus for applying an impervious protective coating over the inside seam of a cylindrical metal can body either before or after the seam is welded, soldered or cemented and prior to spray coating the complete interior of the body. The apparatus is operable to practice the method of intermittently applying an airless spray to the interior seams of the cans as they continuously move past an airless spray gun secured to the end of a stubhorn of a can forming line. The nozzle orifice size and the nozzle orifice pressure are so selected and the nozzle so positioned and controlled that a thin smooth impervious layer of atomized spray is applied over the seam with a minimum of excess material being sprayed onto the seam surface and a minimum of waste material being sprayed past the seam surface.

United States Patent 1191 1111 3,921,570

Hogstrom et al. 1 Nov. 25, 1975 541 APPARATUS FOR STRIPING INSIDE SEAMS 3,104,986 9/1963 Goman et al. 118/2 0F CANS 3,526,027 9/1970 Manuel et al 118/317 x [75] Inventors: Edwin F. Hogstrom, Sheffield;

Burton J- g Amherst, both of Primary ExammerJohn P. Mlclntosh Ohio Attorney, Agent, or F1rm--Wood, Herron & Evans [73] Assignee: Nordson Corporation, Amherst, [57] ABSTRACT Ohio A method and apparatus for applying an impervlous [22] Filed: July 20, 1970 protective coating over the inside seam ofa cylindrical [2]] App No 56 304 metal can body either before or after the seam is welded, soldered or cemented and prior to spray coating the complete interior of the body. The apparatus is 8/ l18/DlG. l0 operable to practice the method of intermittently ap- [51] Int. Cl. 305C 7/02 plying an airless pray to the interior seams of the cans Field of Search 0 as they continuously move past an airless spray gun I l8/DI 10, 8 secured to the end of a stubhorn of a can forming line. The nozzle orifice size and the nozzle orifice pressure [56] References Cited are so selected and the nozzle so positioned and con- UNITED STATES PATENTS trolled that a thin smooth impervious layer of atom- 2 124 853 7/1938 Grupe 118/317 x ized Spray is applied Over the seam with a minimum 113/317 X excess material being sprayed onto the seam surface 2,763,575 9/1956 B 13 302 X and a minimum of waste material being sprayed past 2,895,449 7/1959 Oldfield..... 118/317 X the seam surface.

2,961,990 11/1960 Wruck ll8/2 3,081,947 3/1963 Walter 118/317 x 7 Clams 8 'Dmwmg Figures 2,348,495 5/1944 Peterson SOL SOL CON TROl IRC UIT VALVE L U. a tem Nov. 25, 1975 Sheet1of3 3,921,570

W 39 SOL 2 CONTROL VALVE Al sfia'? w 2 K j Z0 l 55 0 Z5 Xi 76 l w I 1 j MP1 A Edwin F. Hogsfrom BY Burton J. Vila ATTORNEYS US. Patent Nov. 25, 1975 Sheet 2 of3 3,921,570

is /////////e LINVENTORS Edwin F Hpgslfrom BY Burfon J l/llag/ WW4 7%, M

ATTO NEYS APPARATUS FOR STRIPING INSIDE SEAMS OF CANS This invention relates to the application of protective coatings to the interior of cans and more particularly, to the application of protective coatings to the interior soldered, welded or adhered overlapped seam or the butt welded seam of a three piece metal can.

Metal cans are made by either one of two processes. One process, the two piece can process, involves forming a drawn cup from a cylindrical slug of metal and then deep drawing the cup to a can configuration. The other process, the three piece process involves forming a cylindrical can body from a sheet of metal and then attaching two lids or ends to the opposite ends of the body. The invention of this application is concerned only with the application of protective coatings to three piece cans.

In the manufacture of three piece cans, the cylindrical bodies of the cans are formed by wrapping a sheet of metal around a so-called stubhorn. The ends of the sheet are either butted or overlapped and secured together by either a welded seam, a soldered seam, or a cemented seam. The interior of the cylindrical body is then coated with a protective coating which is generally a vinyl lacquer although numerous other materials, as for example, resins, lacquer, waxes and paints are applied for this same purpose, i.e., to afford protection of the contents of the can against contamination by the metal. Particularly beer, beverage and foods must be protected against metal contamination by the application of a tasteless and odorless protective coating material to the interior of the can.

The protective material which is applied to the interior of the can must be continuous throughout the entire interior surface. Any pin holes, cracks or imperfections in the integrity of the coating render the cans unsuitable for most applications. For that reason, excess material is often applied to the interior. That, though, is a wasteful practice and one which is preferably avoided because of the increased cost of the cans when multiplied by the millions and even billions of cans produced by a single company.

One practice generally followed in the can industry to minimize the thickness layer required to be applied to the interior of the can in order to completely cover it is to stripe the interior seam of a three piece can with a first layer of protective material before a second or subsequent layer is applied to the complete interior of the can. It is at the seam that the application of the protective material is most critical and where failures most often occur, generally along the edges of the overlapped seam. Rather than to apply a heavy layer to the complete interior of the can, common practice is to apply a first layer along the seam and then subsequently coat the complete interior of the can with a second layer such that the seam ends up with a double thickness of protective coating material.

At the present time all inside striping is applied by an air spray gun in which the gun remains on and tires atomized lacquer continuously at a spaced line of cans as the cans move past a spray nozzle on a can production line. Because the gun remains on at all times, there is a considerable amount of overspray and waste material.

Additionally, the area is very messy and clean-up is a problem.

There are two principal and partially conflicting criteria applied to astripe of protective material or lacquer on the interior seam of a can. One is that the stripe must be continuous and uniform over the seam so that it completely covers a longitudinal stripe of the can approximately five-eighths inch in width for the full length of the can. The other is that the total weight of material required to effect that coverage must be minimized. Can manufacturers insist that coverage of the stripe be absolute or complete and that there be no pin holes, gaps or cracks in the coating. They also try to minimize the total weight of material required to effect that coverage. At the present time, using the air spray technique, can companies are using approximately 10 milligrams dry weight or cured weight of vinyl lacquer plus or minus 4 milligrams in order to achieve this stripe on a 5 inch long can of 2 or 2% inch diameter. In other words, using, the air spray technique the can companies are averaging approximately 10 milligrams of material per can but there is a very wide range or lack of uniformity in the results in the total weight applied to the cans from. one can to the next. As a result of this relatively poor control, where 6 milligrams would be entirely satisfactory, 14 milligrams or nearly 2 /2 times the material required is often applied and the average amount of material applied averages 40% more than is required. When multiplied by the millions and even billions of cans produced by a single can company, this results in a very large waste of material and a very large expenditure which could be saved if a better application technique were available.

It has been a primary objective of this invention therefore to substantially reduce the application of excess material to an inside striped seam of a can in order to obtain a uniform continuous coating of protective material or lacquer over the seam. Otherwise expressed it has been a primary objective of the invention to reduce the total weight of material required to completely cover a seam by improving the consistency of material weight from one can to the next while still obtaining a uniform thickness of material over the seam of the can.

Another objective of this invention has been to reduce or eliminate the clean-up problem which results from over spraying the can and spraying material onto the rails over which the cans ride as they are sprayed.

These objectives are accomplished and one aspect of this invention is predicated upon the concept of utilizing an airless spray to apply the protective coating to the inside seam of a can. When this technique is successfully applied, it can effect as much or more than a 50% savings in total weight of material applied to the interior seam of a can while still obtaining a perfectly uniform coating of the seam.

Airless spray is a well known spraying technique which is very distinct and different from conventional air spray. It involves forcing a liquid material through a generally elliptical shaped orifice at high pressures, i.e., on the order of from 200 to 1000 psi with the result that the spray fans out after emerging from the orifice and breaks up into an atomized spray without the impingement of any air stream against it.

The conventional air spray on the other hand involves extruding a low pressure stream of paint or liquid material from a nozzle at a pressure of from 10 to 50 psi and impacting that extruded stream with a high pressure stream of air (on the order of 35-75 psi) to atomize it and convert it into a spray.

Airless spray has the advantage over air spray of giving much better spray control and deposition efficiency in that the spray is confined to a much smaller area and does notfog or contaminate the area surrounding the application surface to the same degree as does the air spray technique. It applies a more consistent, even pattern of sprayed material than does air spray.

Because of the density of airless spray, it cannot be left on continuously, as is the air spray, without a very appreciable waste of material. Consequently, another aspect of this invention is predicated upon synchronizing the airless spray with high speed movement of the cans past the spray nozzle so that the spray is turned off when a space between cans is located opposite the nozzle. To effect that high speed operation, a check valve is located immediately adjacent the nozzle orifice to open and close the orifice in synchronization with movement of the cans past the orifice. There is also a high speed control for accurately and precisely controlling opening and closing movement of that check valve in synchronization with the high speed movement of the cans past the orifice.

In order to obtain the necessary degree of control to utilize airless spray to apply a stripe of protective material over the interior seam of a can, the complete spray gun including the check valve and the motor for opening and closing the check valve must be located interiorly of the can so that the cylindrical cans pass over the gun. In the case of the majority of cans, i.e., those of 2 or 2 /2 inch diameter, there is a severe space problem because of the inability to locate the orifice nozzle more than approximately 1 inch from the seam to which the stripe of protective material is to be applied. As airless spray emerges from a nozzle orifice it is a fan shaped sheet of material. This fan then ripples and breaks up into ligaments as the fan spreads and the ligaments then break up into an atomized spray. To apply the stripe of material in a sufficiently thin film to meet the requirements of the can industry as well as to maintain the uniformity of the stripe, the nozzle must be located a sufficient distance from the seam to allow the emerging spray to break up into atomized droplets. Heretofore, airless spray has been used to apply stripes to the outside seams of cans but in those applications, the nozzle orifice has been located approximately 2 /2 inches from the seam. That spacing is not available, though, when a stripe of protective material is applied to the interior of a can.

Another aspect of this invention is predicated upon the empirical determination that a satisfactory thin atomized airless spray may be evenly and uniformly applied in a stripe to a can when the nozzle orifice is positioned 1 inch or less from the application surface or substrate if the nozzle orifice size and the pressure of the material in the nozzle are maintained within a critical range. Specifically, one aspect of this invention is predicated upon the determination that the spray may be sufficiently atomized in a very short distance so as to obtain a uniform thin layer or film of protective material over the seam if a very small nozzle orifice is used in combination with low pressure emergence of the spray from the nozzle.

Nozzle orifice size is measured in terms of the quantity of water which flows through the orifice at 500 pounds per square inch and at room temperature. It has been determined empirically that a nozzle orifice which has a flow rate of 0.015 gallons per minute of water at 500 psi is suitable for this application if the pressure of the spray emerging from the nozzle is maintained very low or just above that pressure at which the spray will break up into an atomized spray, i.e., at approximately 350 pounds per square inch. At the present time this is the smallest spray orifice commercially available. If the pressure is reduced substantially below 350 pounds per square inch, the resulting spray will not break up into an atomized spray and therefore cannot be applied to a substrate in a sufficiently thin film of sufficient uniformity to match or improve over conventional air spray techniques used in the industry today. If either the nozzle orifice or the pressure is increased substantially above these values, the film either becomes too inconsistent or too heavy to satisfy can industry requirements.

These and other objects and advantages of this invention will be more readily apparent from the following description of the drawings in which:

FIG. 1 is a diagrammatic illustration of a can body production line including the novel inside striping mechanism of this invention;

FIG. 2 is an enlarged side elevational view of the can striping mechanism of this invention;

FIG. 3 is an end elevational view of the striping mechanism of FIG. 2;

FIG. 4 is a cross-sectional view taken vertically through the spray gun nozzle and adapter of FIG. 2;

FIG. 5 is a cross-sectional view taken horizontally through a portion of the spray gun nozzle and adapter of FIG. 2 and illustrating the gun in the open condition;

FIG. 6 is an enlarged side elevational view of the spray emerging from the nozzle; and

FIG. 7 is a cross sectional view taken along lines 77 of FIG. 3 illustrating the manner of application of the spray to the can seam; and

FIG. 8 is a chart of comparative conditions and results using airless and air spray to stripe the inside seam of can bodies.

Referring first to FIG. 1 there is illustrated diagrammatically a standard can production line used in the production of cylindrical can bodies. This line includes a stubhorn 10 which acts as a mandrel around which can bodies 11 are formed as they pass downstream over the stubhorn. The can bodies 11 are moved longitudinally over the stubhorn from a magazine 12 by lugs of a chain conveyor which engage the rear edge 13 of the bodies and push the bodies along the stubhorn. As the bodies pass off the stubhorn, after having been formed into a cylindrical configuration they move into a network of rails through which the bodies pass during continued formation of the can.

In the final stages of movement of the can bodies over the stubhorn 10 the ends of the sheet metal from which the body is made are overlapped or joined. If the bodies are to be seamed by adhesive or by a solder the solder or adhesive is placed in the overlapped seam at a seaming station indicated by the numeral 14. As the bodies pass off of the stubhorn l0 and into the rails 15, they are crimped and pass through an inside striping station indicated by the numeral 16. At this station, a stripe of protective material 17 is sprayed over the overlapped seam 18 of the can.

In order to apply the stripe 17 of protective material over the seam of the can, a spray gun 20 is secured to the end of the stubhorn. This gun is so positioned that the can bodies pass over it before passing into the rails 15.

The gun is secured to the end surface 21 of the stubhorn by a generally U-shaped bracket 22 secured onto the end of the stubborn by a plurality of bolts 23. Bolts 19 similarly secure the gun to the opposite or downstream end 24 of the bracket 22.

In one preferred embodiment, the spray gun 20 is of the so-called circulating flow type, that is there is a continuous flow of fluid or coating material to the gun through a fluid inlet line 25. There is also a continuous flow of fluid or lacquer from the gun via line 26. As a result of this continuous flow, the temperature of the fluid or lacquer may be maintained constant in the gun even when the gun is not in use and the fluid would otherwise be stationary in the gun. Since some lacquers or can protective materials are applied at a temperature substantially above room temperature, it is important that these lacquers not be permitted to stand and become hardened in the gun. The circulating flow of fluid through the gun precludes this hardening or setting of the lacquer. In the case of other lacquers which are applied at ambient or room temperature, temperature control is not important and a conventional non-circulating or one fluid line gun may be used.

The gun 20 contains a check valve indicated gener ally by the numeral operable to open and close a passage 61 leading to an orifice 31 of a nozzle 29 in synchronization with movement of cans past the orifice 31. The check valve is pneumatically opened by air pressure supplied to the gun via an inlet line 32 and is spring biased to a closed position. Air pressure at approximately 60 psi is supplied to the air inlet line 32 from an air pressure source 33 through a solenoid controlled valve 34. An electric photocell circuit including a photocell sender 35 and receiver 36 control the flow of electric current to the solenoid of the valve 34. The photocell sender 35 and receiver 36 are located at or near the can striping station adjacent the end of the stubhorn and direct a light beam through a hole 37 in the stubhorn so that cans entering the striping station break the circuit and trip the solenoid valve 34, thereby causing the valve 34 to be opened and air pressure supplied via line 32 to the gun.

The solenoid valve portion of the valve 34 is an onoff solenoid valve 39. It is used in combination with a conventional four way spool valve 42, to one end of which air is alternately supplied from the source 33 at a pressure of approximately 60 psi or to which air is vented to atmosphere under the control of the solenoid. Air at a lesser pressure, as for example 20 psi is supplied through the line 38 to the opposite end of the spool at all times so that when the solenoid electrical circuit is broken, the solenoid valve connects the high pressure end of the spool valve 42 to atmospheric pressure and the low pressure (20 psi) at the opposite end then moves the spool toward the high pressure end. When the electrical circuit again energizes the solenoid, the solenoid valve 39 connects the high pressure end of the spool to 60 psi and the spool immediately moves toward the low pressure end against the resistance offered by the low pressure in line 38. It has been found that the valve 34 may be more reliable with the low pressure line connected to the one end of the valve than it is when it utilizes a spring return. It has also been found that the solenoid valve may be fast enough acting when used as pilot valve to control flow to the gun but that if used with higher flow capacities without the second stage spool valve 42, it is too slow to keep up with current can production lines.

Referring now to FIGS. 4 and 5 it will be seen that the gun 20 generally comprises a two piece cylindrical body 40 within which there is an axial or central bore 41. This bore comprises a fluid chamber 43 adjacent the front end of the body, a smaller diameter connecting chamber 44 and a large diameter piston chamber 45. The rear side of the piston chamber 45 is opened to the atmosphere through a small diameter section 46 of the bore 41 connected to the piston chamber 45 via an intermediate diameter chamber 47. An end cap 48 is secured to the body by bolts (not shown) and closes the fluid chamber 43. The cap 48 comprises a central disc 49 from which hub sections 50., 51 extend rearwardly and forwardly, respectively. The rearward hub 50 fits within, and with an O-ring, seals the fluid chamber 43. The forwardly extending hub section 51 is threaded on its exterior as indicated at 54 and has an inwardly ex tending flange 55. An axial bore 56 extends through the cap 48. It comprises a large diameter rear section 57 and a smaller diameter front section 58.

A cylindrical metal insert 59 made from a hard material, as for example, tungsten carbide, is brazed or otherwise fixedly secured within the small diameter section 58 of the cap. This insert defines the seat of the check valve 40. It has a stepped axial bore which comprises a large diameter rearward! section 60 and a small diameter passage 61 interconnected by a shoulder 62. An arcuate seat 63 is machined into the shoulder at the point where the shoulder joins the small bore 61. The seat is conflgurated as an annular taper so as to cooperate with a generally semispherical end 65 of the check valve head 66 to form a seal.

A locking sleeve 70 is threaded onto the externally threaded section 54 of the hub 51. This locking sleeve is secured to the adapter by a retaining ring 71 which is secured in a groove in the body 77 of the adapter 75.

Referring to FIG. 3, it will be noted that the gun 20 is mounted with its longitudinal axis aligned coaxially with the longitudinal axis of the stubhorn 10. The nozzle orifice 31 of the gun is positioned a distance D laterally offset from the seam containing diametral plane 80 of cans passing over the gun so as to enable the stream of spray emitted from the nozzle orifice to be angulated onto the generally radial edge 83 of the can which results from overlapping the seam. It has been found that the top and bottom corners 84, 85 of this edge are most commonly the points of failure of the coating. By offsetting the nozzle orifice laterally the distance D or approximately three-eighths inch in the case of a 2 inch diameter can from the seam containing diametral plane 80 of the can and then directing the nozzle back toward the seam at an angle of approximately 12 to a vertical plane, these edges are satisfactorily covered by the spray.

Airless spray is generally created by directing a high pressure stream of fluid through a generally elliptical shaped orifice 31. The pattern which the spray assumes as it emerges from the orifice is depicted in FIGS. 6 and 7. Upon emerging from the nozzle at a pressure of from 200l ,000 psi, the spray spreads out or fans out to form a generally fan-shaped solid curtain of lacquer. This curtain is depicted in FIG. 6 by the numeral 86. As the curtain moves away from the nozzle ripples or waves form in it as indicated by the numeral 87. The ripples then break up into longitudinal ligaments indicated by the numeral 88. These ligaments. subsequently break up as they move away from the nozzle into droplets 89 which then atomize into a fine spray 90. As viewed in cross section the pattern of atomized spray 90 is elliptical in configuration as indicated by the dotted line pattern illustrated in FIG. 7.

If vinyl lacquer is properly applied to a can body which is inches in length, a uniform continuous film five-eighths inch in width will, after curing or when dry, weigh only 6 milligrams. In order to apply a sufficiently thin film of lacquer or any other protective coating material to the seam of a can by the airless spray technique, the film must be atomized as indicated at 90 before it strikes the can surface. Consequently, the nozzle orifice must be maintained a sufficient distance away from the can surface to permit the spray to go through the wave, ligament, droplet and atomization stages before striking the can. For that reason, the adapter 75 is located between the check valve and the nozzle orifice 31. This adapter offsets the nozzle orifice away from the can seam as well as angulates it relative to the seam.

As may be seen in FIGS. 3 and 4, the axis 76 of the nozzle orifice is angulated at approximately 12 to a vertical plane through the orifice and parallel to the longitudinal axis of the cans. It is angulated forwardly approximately 68 to the longitudinal axis of the cans in the seam containing diametral plane of the can. On small cans, the nozzle orifice is located as far away as practical fromthe seam so as to allow a sufficient distance for atomization of the lacquer or protective material before it strikes the can. The adapter 75 which permits this offset and this angulation of the nozzle axis 76 relative to the seams of the cans comprises an axial body section 77 and an offset forward end section 78. The end section 78 has an arcuate peripheral surface 79 and a planar inside surface 74. This planar inside surface or platform 74 is angulated at an angle of approximately l2 to an axial horizontal plane when measured in a vertical plane normal to the diametral plane 80. It is also angulated at an angle of 22 to this same horizontal plane when measured in a vertical plane through the axis of the spray gun 20. The nozzle 29 is mounted normal to the planar platform surface 74.

The end section 78 of the adapter has a bore 95 normal to the planar surface 7 4. This bore 95 is intersected by a narrow conduit or passage 96 which extends between the bore 95 and the radial end surface 97 of the axial section 77 of the adapter. The passage 96 terminates or intersects the end surface 97 on the axis of that axial section. It therefore communicates with the axial passage 61 in the check valve seat 63. The inner end of the bore 95 is threaded to receive the externally threaded nozzle body 135.

As may be seen most clearly in FIG. 6, the nozzle body 135 has a stepped axial bore, the largest diameter end portion 137 of which is internally threaded for reception of an externally threaded turbulence plate 98. This plate has an axial bore 138 which communicates with a radial bore 139 in a small diameter nose portion 140 of the turbulence plate 98. The radial bore 138 opens into a fluid chamber 141 which surrounds the nose portion 140 of the turbulence plate and the inner end 142 of a nozzle tip 143. An axial passage of this tip or so-called approach passage 146 extends from the nozzle orifice 31 back to the rear surface 142 which abuts the front surface 145 of the turbulence plate. A very shallow narrow groove 147 extends diametrally across the front face 145 of the turbulence plate and connects the approach chamber 146 to the fluid chambet 141. This small groove 147 through which liquid must pass before entering the approach chamber 146 has the effect of reducing the pressure of liquid emerging from the nozzle orifice 31. In actuality, the turbulence plate 98 reduces the pressure in the approach chamber 146 of the nozzle tip approximately -100 pounds below the gauge pressure of the liquid behind the plate. A more complete description of the nozzle 29 and of the turbulence plate may be found in copending application Ser. No. 731,062, filed May 22, 1968 of E. T. Nord et al., which application is assigned to the assignee of this application, and which application is hereby incorporated by reference for purposes of completing this disclosure.

Referring back again to FIGS. 4 and 5 it will be seen that the check valve head 66 is controlled in its movement into and out of engagement with the check valve seat 63 by the pneumatic piston 105. This piston is connected to the head end of the check valve by a connecting rod 106. A conventional threaded coupling and lock nut 104 enable the rod 106 to be adjusted in length relative to the head 66. A compression spring 107 normally biases the head and connected piston rod 106 to the right as viewed in FIG. 4 to a position in which the check valve 30 is seated or closed. This spring 107 bears at one end against the nut 104 and at the opposite end against a collar 108 which is fixedly seated in the chamber of bore 41 and has a shoulder or flange 109 seated against a shoulder 1 10 of the bore 41. O-rings 111 and 112 seal the liquid chamber 43 from the pneumatic chamber 45, and vice versa. The forward end 115 of the piston chamber 45 is also sealed from the rear portion 1 16 by a pneumatic seal 117 located around the periphery of the piston 105. The piston is secured onto the end of the rod 106 by a pair of lock nuts 118 and 119 threaded onto the threaded innermost end 120 of the rod 106. As may be seen most clearly in FIG. 5, air under shop pressure, e.g., approximately 60 psi is supplied to the inner chamber 115 of the piston chamber 45 from the fluid line 32 via a connecting passage 121 in the body 40 of the gun 20. Flow of air in the line 32 and thus in the passage 121 is controlled by the solenoid valve 34 as explained more fully hereinafter.

As may be seen most clearly in FIGS. 4 and 6, the nozzle orifice 31 is generally elliptical in configuration when viewed in a direction parallel to the axis of the nozzle. It is made by making a cut into a generally hollow hemispherical shaped nozzle of substantially uniform wall thickness. The cut is generally made by a grinding wheel which has a tapered edge. The manner in which the cut is made and the nozzle is produced is fully explained in copending application Ser. No. 13,598 of William S. Stumphauzer et al., which is assigned to the assignee of this application. This nozzle lays down a generally fan shaped elliptical spray pattern 26 as may be seen most clearly in FIG. 7. The width W of the stripe 17 of protective material 125 laid down or applied over the overlapping seam 18 of the can 11 may be controlled by angulating the elliptical pattern relative to the longitudinal axis over the seam of the can. In the embodiment illustrated in FIG. 7, the longitudinal axis 126 of the elliptical pattern is angulated approximately 55 relative to the longitudinal axis of the seam 18. This has the net effect of reducing the width of the pattern approximately 85% over what it is with the long axis 126 of the pattern normal to the longitudinal axis or seam of the can.

In operation, can bodies 11 are formed over the stubhorn at the rate of approximately 550 i 50 cans per minute. This rate varies from one can manufacturer to another but quite commonly today averages approximately 575 can bodies per minute per line in the production of standard 2 or 2 /2 inch diameter cans of 4 13/ 16 inch length. As the cans move along the stubborn a solder, adhesive or weld iscommonly applied to the overlapping or abutting edges of the sheet at a seaming station 14. This station is located immediately in front of the striping station 16 where the stripe of protective material from the nozzle 29 and spray gun 20 is directed onto the seam. In the case of soldered cans, the seam is subsequently completed and the striping material simultaneously cured by the application of heat to the edge at a subsequent soldering station. In the case of seam welded or seam adhered cans, the striping material is either heat or air cured at a much lower temperature further down the can production line.

The emission of liquid spray from the nozzle 29 is turned on and off in synchronization with movement of the can bodies 11 over the stubhorn and through the striping station. This is accomplished by the can body interrupting a light beam of the photocell sender and receiver unit 35, 36. Upon interruption of this light beam and after a predetermined time delay built into a solenoid control circuit, the solenoid control circuit is operable to shift the solenoid and move a valve spool of the valve 34 so as to connect the air line 32 to the source of air pressure 33, thereby connecting the forward end chamber 115 of the check valve control piston chamber to high pressure, i.e., 60 psi air. This results in movement of the piston 105 and opening of the check valve 30. Upon opening of this valve the liquid protective material in the fluid chamber 43 is allowed to pass from the fluid chamber 43 past the head of the valve into the conduit or passage 61 and subsequently to the nozzle orifice 31 of the nozzle 29. Liquid in the chamber 43 is maintained at a pressure approximately 475 psi, the pressure at which it is supplied by a pump 131 from a reservoir 130. In passing through the nozzle, the pressure of the liquid is reduced approximately 100 psi by the turbulence plate 98.

A predetermined time after interruption of the light beam, that can which had broken the light beam passes out of alignment with the nozzle 29. After that predetermined time, a timer circuit interrupts the signal to the solenoid, causing it to be deenergized and the control circuit to be reset preparatory to interruption of the light beam by the next following can. Upon deenergization of the solenoid, low air pressure, i.e., 20 psi, in line 38 then moves the spool of the valve 34 to the position in which the air line 32 is connected to atmospheric pressure. This results in the spring 107 of the gun causing the check valve to be closed, which im mediately cuts off the flow of spray from the nozzle until the next following can again interrupts the light beam. 0

The primary advantage of this airless spray technique in the application of inside seam striping is the substantial savings of material which it effects overconventional air spray techniques commonly employed today.

Examples of these savings are depicted in the chart of FIG. 8. Referring to that chart, one conventional air spray application is depicted in Column 1. This application involves the striping of an inside can seam with an air spray of a commercially available vinyl lacquer, Mobile Chemical Company S-6838-0l5. In this appli- 10 cation, a stripe of protective material is applied to a 2 /2 inch diameter can approximately 4 13/16 inches in length. Standard practice using the air spray technique is to apply 14 milligrams of material with a tolerance of i 4 milligrams. The conditions under which that material is applied are given in the chart. Specifically, the air spray is applied at ambient temperature or at approximately 77 F. At this temperature the material has a viscosity of 16 seconds in a Ford No. 4 cup. It is continuously sprayed on cans moving at a speed of approximately 550 cans a minute past the air nozzle which is operative to lay down a stripe five-eighths inch in width for the length of the can. The nozzle utilized is 0.012 inch in diameter and material is forced through the nozzle at a pressure 12-15 psi. The air pressure utilized to break up or atomize the spray is at approximately 35-40 psi. These conditions in one can company application resulted in a stripe which weighed 14 milligrams i 4 milligrams after curing.

Three other applications involving airless spray of commercial protective material. to the inside seam of a can are depicted in Columns 2, 3 and 4 0f the chart. These applications all average after curing approximately 5 milligrams of material to cover the same size can with the same or a greater degree of protection. This amounts to approximately a 50% savings in the material applied to the seam. The airless spray technique because it is turned off as the cans pass the nozzle during that interval of time when a space between cans is located opposite the nozzle, also minimizes overspray or the application of spray to areas around a target substrate. It has been found that the problems of clean up and contamination of the spray area are also minimized using the airless spray technique in this application. As is evidenced in the chart, the optimal conditions which have been found to be applicable to airless spray for this inside seam application generally require a nozzle size of 0.015 gallons per minute flow of water at 500 psi. The nozzle orifice pressure is usually maintained at approximately 350 psi. Under these conditions the spray is sufficiently atomized in a short distance to apply a thin even protective coating to the seam. If the nozzle orifice is greater than 0.040 gal/min. water at 500 psi or the nozzle orifice pressure exceeds 600 psi operating on a can line moving at a rate of approximately 550 cans per minute past the nozzle, it has been found that in the application of almost all protective coatings or at least all of those that have been tested the resulting coating is too heavy to be practicable and is too prone to blister and crack to be commercially acceptable. Of course, as the speed of the can line increases above the current upper limit, i.e., approximately 550 cans per minute, higher flow rates may be tolerated.

As is evidenced in Columns 2, 3 and 4 of the chart of FIG. 8, the optimal conditions under which airless spray is used to stripe the inside of cans is identical for the three different protective materials depicted therein. The three different protective materials are an air cure epoxy resin material, Mobile Chemical Company 69-X-l6l (Column 2), a heat cure epoxy resin material, Mobile Chemical Company S-412 l-008 (Column 3), and the same vinyl lacquer material depicted in Column 1, Mobile Chemical Company 8-6838-015 vinyl lacquer (Column 3). The viscosities of all three materials differ but the conditions under which they applied are generally the same. Specifically, airless examples 1 and 3 are both applied at a temperature of 150l70 F. to a line of cans moving at the rate of approximately 550 cans per minute past the spray nozzle. The second example is applied at ambient temperature. This rate of movement varies from line to line and even within each line as the conditions under which the line operates varies. The cans utilized in the example of the chart all have a seam stripe area /8 inch in Width X 4 13/16 inches in length. The gauge pressure or the pressure of the material in the chamber 43 behind the nozzle turbulence plate is preferably approximately 475 psi. In the three airless spray examples, the pressure at the nozzle orifice 31 is 350 psi but may vary by 50 psi in either direction depending upon temperatures, pressures and viscosity of the material. The preferred nozzle is sized such that it has a flow rate of 0.015 gallons per minute of water at 500 psi. This is a very small spray nozzle for the application of airless spray. These conditions result in a stripe being applied to the seam of the can which has a total dry or cured weight of 6 milligrams. It varies by approximately 1 milligram in either direction from that mean value.

It will be readily apparent from the chart that the airless spray technique substantially reduces the total weight of material required to completely and uniformly cover the seam of a can. It will also be seen that the degree of control exercisable over the thickness or weight of that layer in a uniform nonporous film is much greater or otherwise expressed may be much more closely controlled than the application of conventional air spray.

While only one preferred embodiment of this invention has been described in detail herein those persons skilled in the art to which this invention pertains will readily appreciate numerous changes and alterations which may be made without departing fromthe spirit of this invention. Therefore 1 do not intend to be limited except by the scope of the appended claims.

Having described my invention, 1 claim:

1. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body,

means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies.

means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and

12 said airless spray nozzle orifice having a flow rate of less than 0.040but more than 0.010 gallons per minute of water at 500 pounds per square inch pressure.

2. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body,

means for forcing an airless spray fan of liquid coating material at a pressure of about 350 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies,

means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and

said airless spray nozzle orifice having a flow rate of about 0.015 gallons of water per minute at 500 pounds per square inch pressure.

3. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body,

means for forcing an airless spray fan of liquid coating material at high pressure from the nozzle orifice and directing in onto the interior surface of the seams of the can bodies,

means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, said means for starting and stopping the emission of airless spray from the nozzle comprising a spray gun attached to a stubhorn of the can forming line and including a check valve located in the spray gun immediately adjacent the nozzle orifice, said 13 spray gun including a pneumatic motor for effecting movement of the check valve.

4. The apparatus of claim 3 which further comprises an electronic control circuit including a photocell circuit to control operation of the pneumatic motor.

5. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can forming line over which can bodies are formed into cylinders at a rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less an 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray gun including a spray nozzle,

means for securing the spray gun on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice onto the interior surface of the seams of the can bodies,

means including a check valve located interiorly of the spray gun for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and

said airless spray nozzle orifice having a flow rate of less than 0.040 but more than 0.010 gallons per minute of water at 500 pounds per square inch pressure.

6. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can forming line over which can bodies are formed into cylinders at a rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray gun including a spray nozzle,

means for securing the spray gun on a can assembly line in a position in which the nozzle is located inte- 14 riorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of about 350 pounds per square inch from the nozzle orifice onto the interior surface of the seams of the can bodies,

means including a check valve located interiorly of the spray gun for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and

said airless spray nozzle orifice having a flow rate of about 0.015 gallons of water per minute at 500 pounds per square inch pressure.

7. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station, which striping station is located at the end of a stubhorn over which can bodies are formed into a cylinder at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle to the end of a stubhorn on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body,

the orifice of said spray nozzle being sized so that it has a flow rate of less than 0.040 but more than 0.010 gallons per minute of water at 500 pounds per square inch,

means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies, and

means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice. 

1. Apparatus for appLying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies. means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and said airless spray nozzle orifice having a flow rate of less than 0.040 but more than 0.010 gallons per minute of water at 500 pounds per square inch pressure.
 2. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of about 350 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies, means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and said airless spray nozzle orifice having a flow rate of about 0.015 gallons of water per minute at 500 pounds per square inch pressure.
 3. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can body forming line over which can bodies are formed into cylinders at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at high pressure from the nozzle orifice and directing in onto the interior surface oF the seams of the can bodies, means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but it is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, said means for starting and stopping the emission of airless spray from the nozzle comprising a spray gun attached to a stubhorn of the can forming line and including a check valve located in the spray gun immediately adjacent the nozzle orifice, said spray gun including a pneumatic motor for effecting movement of the check valve.
 4. The apparatus of claim 3 which further comprises an electronic control circuit including a photocell circuit to control operation of the pneumatic motor.
 5. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can forming line over which can bodies are formed into cylinders at a rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less an 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray gun including a spray nozzle, means for securing the spray gun on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice onto the interior surface of the seams of the can bodies, means including a check valve located interiorly of the spray gun for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice, and said airless spray nozzle orifice having a flow rate of less than 0.040 but more than 0.010 gallons per minute of water at 500 pounds per square inch pressure.
 6. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station of a can forming line over which can bodies are formed into cylinders at a rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray gun including a spray nozzle, means for securing the spray gun on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, means for forcing an airless spray fan of liquid coating material at a pressure of about 350 pounds per square inch from the nozzle orifice onto the interior surface of the seams of the can bodies, means including a check valve located interiorly of the spray gun for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can bOdy moves into alignment with the orifice, and said airless spray nozzle orifice having a flow rate of about 0.015 gallons of water per minute at 500 pounds per square inch pressure.
 7. Apparatus for applying an impervious protective coating to the longitudinal seams of spaced cylindrical can bodies as the can bodies move through a striping station, which striping station is located at the end of a stubhorn over which can bodies are formed into a cylinder at the rate of at least 300 can bodies per minute, which apparatus comprises coating means for applying a continuous impervious coating of less than 1.5 milligrams per linear inch to the longitudinal seams of said can bodies, said coating means including an airless spray nozzle, means for securing the nozzle to the end of a stubhorn on a can assembly line in a position in which the nozzle is located interiorly of the cans and has its orifice directed toward the interior of a seam of a formed body, the orifice of said spray nozzle being sized so that it has a flow rate of less than 0.040 but more than 0.010 gallons per minute of water at 500 pounds per square inch, means for forcing an airless spray fan of liquid coating material at a pressure of less than 600 pounds per square inch but more than 200 pounds per square inch from the nozzle orifice and directing it onto the interior surface of the seams of the can bodies, and means for starting and stopping the emission of airless spray from the nozzle orifice in synchronization with movement of the spaced can bodies past the nozzle so that the airless spray is directed onto a seam of a can body as the body passes the nozzle orifice but is turned off after that can body passes the nozzle orifice until the seam of the next following can body moves into alignment with the orifice. 